己烯糖醛酸的选择性水解及其对纸浆漂白的影响

Selective Hydrolysis of Hexenuronic Acid and Its Effects on Pul

在硫酸盐法制浆中，聚木糖的４—Ｏ—甲基葡萄糖醛酸主要转变为己烯糖醛酸（ＨｅｘＡ）。ＨｅｘＡ能与一些亲电性的漂白剂，如氯气、二氧化氯、臭氧和过醋酸等反应，增加漂白化学药品的消耗。ＨｅｘＡ还能与高锰酸盐起反应，影响纸浆Ｋａｐｐａ值。ＨｅｘＡ也是纸浆中过渡金属离子如锰离子螯合的主要部位。对硫酸盐浆进行温和的酸水解，能除去浆中的己烯糖醛酸，而其它碳水化合物只有很少量被溶解或降解。在ＥＣＦ或ＴＣＦ漂白中，引入酸水解处理，选择性地除去己烯糖醛酸，可减少漂白药品消耗，提高纸浆白度稳定性，Ｋａｐｐａ值降低１～６个单位，金属离子含量大大降低。

In kraft pulping, a major portion of 4Omethyl glucuronic acid groups are converted to 4 deoxy hexa 4 enuronic acid groups(HexA). HexA will react with a number of electrophilic bleaching chemicals, such as chlorine dioxide, ozone and pexacids, thus consuming some of the chemicals that should be used for bleaching. HexA is also vulnerable to permanagnates, indicating that erroneous determination of kappa number for pulps may happen. Hexenuronic acid presents itself with strong cheating sites in kraft pulps for transition metal ions, such as manganese cation. If HexA is selectively removed through a mild acid hydrolysis of the kraft pulp, only traces of other carbohydrates dissolved. The selective hydrolysis of HexA can be applied for ECF and TCF bleaching of kraft pulps. The advantages gained include lower bleaching chemical consumption and higher brightness stability of bleached pulp.At the same time ,a more reliable kappa number can be determined for the pulps. Reduction of 1～6 units in kappa number is not uncommon, as transition metals are significantly removed from the pulp through the selective hydrolysis of HexA.